A pervasive characteristic of mental retardation is response slowness and variability. Research utilizing the reaction time (RT) model has implicated attending/arousal functions and response performance as sources of this characteristic. The proposed research will measure the component physiological latencies (evoked potentials, muscle potentials) in the stimulus-response chain. Each of these components, and the RT will be manipulated by procedures designed to affect each one differentially. This will isolate those components in the slow retardate and normal which contribute to slowness and variability. Motor potentials will also be explored for clues to RT slowness. BIBLIOGRAPHIC REFERENCES: Warren,C., Karrer, R. & Ruth, R. Slow potential activity of the brain preceding movement in the mentally retarded. 4th Internat'l. Congress on Event Related Slow Potentials of the Brain. 1976 (In Press). Karrer, R., Warren, D., Ruth, R. & Gillett, J. Pre-motion potentials during the development of motor differentiation in children. Psychophysiology, 1976, 13, 183.